In the conventional systems using electric currents, rotary switches have been known and, more recently, electromechanical systems of the "cross-bar" type or solely electronic systems, always aiming to ensure electric continuity between two conductive elements selected from among a number of others.
In systems with light signals transmitted by optical fibers, it is possible to use electronic switches, but they are particularly difficult to construct for operation at the required frequencies. There are also known devices for solely optical switching consisting in putting into direct selective connection two given optical fibers without the aid of an intermediate electronic transformation.
In this case, one solution is to proceed by material displacement of at least one of the fibers to be connected, in order to bring the core of one strictly opposite the core of the other to ensure continuity of light transmission. U.S. Pat. No. 4,204,744 discloses such a solution.
It is alternatively possible to use, between the fibers to be connected, devices for collimation and refocusing, together with intermediate mobile prism systems for displacing the parallel beam in a direction parallel to its own and thus the final point of re-focusing on the core of the receiving fiber.
However, all these devices require high precision mechanical movements. In fact, the core diameter of the most usual optical fibers is between 0.1 and 0.01 mm, for example of the order of 0.05 mm. The relative positioning of the fibers to one another or of a fiber relative to its image must then be ensured with a precision of the order of a micron. Mechanical systems ensuring either the displacement of the fibers themselves or the displacement of the deviating prisms are therefore particularly intricate to construct and consequently very costly.